Hybrid two-dimensional correlation infrared spectrum of reversibility of thermal-induced phase transition of poly (N-isopropylmethacrylamide) in aqueous solutions

Temperature-induced reversibility of coil-globule transition was studied for poly (N-isopropyl-methacrylamide) (PNiPMA) in aqueous solutions by means of Fourier transform infrared (FTIR) spectroscopy and hybrid two-dimensional (2D) correlation spectroscopy. The degree of the symmetry along the diagonal line for PNiPMA in sample-sample (SS) hybrid two-dimensional IR correlation spectrum which was constructed from IR spectra measured in heating and cooling processes reflects the recovery rate of original species, transition temperature, and the rate of the concentration changes during the phase transition. The present study demonstrates a novel application of hybrid two-dimensional correlation spectroscopy in exploring the reversibility of phase transitions in polymer, such kind of study has a great potential application to revealing the phase transition dynamics and molecular interactions of polymers and proteins.